1. Field of the Invention
The present invention relates to an air bag that is folded and housed in a boss positioned in the vicinity of the center of a ring of a steering wheel gripped by a driver during steering.
2. Description of the Related Art
Conventionally, an air bag for steering wheel includes a driver side wall disposed on the driver side of the completely inflated air bag and a wheel side wall disposed on the steering wheel side of the completely inflated air bag. The driver side wall and the wheel side wall are substantially equal in outer shape to each other. An opening for supplying inflation gas therethrough is disposed in the vicinity of the center of the wheel side wall. The periphery of the opening provides an area for attachment of the air bag to a steering wheel. Besides, in the vicinity of this opening is a tether for regulating a separation distance between the driver side wall and the wheel side wall of the completely inflated air bag and thus regulating the thickness of the completely inflated air bag (e.g., see JP-A-2002-012111).
However, in the conventional air bag for steering wheel, in the course of inflation, an area in the vicinity of the outer periphery sometimes oscillates in an up and down direction (an up and down direction along the axial direction of a steering shaft obtained when the steering wheel is mounted on a vehicle). When such a situation is fatal, the driver moves forward with the area of the outer periphery of the air bag separated upwardly from the ring, thus inviting a situation in which the driver directly contacts the ring. That is, variations occur in the holding performance of the air bag, so that the conventional air bag has left room for improvement in preventing the oscillations in the course of inflation.